The present invention relates to an image forming apparatus such as a digital copying machine, wherein an image on a document is read and subjected to an image process, obtained image data is accumulated on a memory, and an image is formed by using a laser electrophotographic process.
A digital copying machine has the following structures and functions. After a document is read by optical means, the read image is converted to an electric signal and subjected to various image processing. Then, image data is accumulated on a memory or processed, and the image is reproduced from the data by using a laser electrophotographic process.
Since the digital copying machine has the above structures and functions, the following applications are possible, in addition to the copying functions of a conventional analog copying machine. For example, the digital copying machine may be connected to a public line to perform facsimile functions. Specifically, it may transmit images to the public line or may receive images from the public line to print out them. Moreover, the digital copying machine may be provided with image communication means for communication with a host computer, whereby print data is received and printed out by using a single laser electrophotographic process (laser engine).
In an image forming process in the digital copying machine, after a document is read by optical means, an optical signal of the read image is converted to an electric signal by using a photoelectric conversion element such as a CCD. The electric signal is subjected to various image processes, such as an analog/digital conversion process, linear/non-linear filtering processes, a frequency conversion process using a line memory for a one-line image component, an enlargement/reduction process, and a gray-scale process. The image is them reproduced from the obtained data by using a laser electrophotographic process.
Furthermore, using the features the digital copying machine, the following functions can be performed. For example, a memory copy function is performed, wherein the processed image signal is stored in a two-dimensional memory (page memory) for a one-page image and the content of the memory is repeatedly read out and printed. An electronic sorting function is performed, wherein the image signals stored in the page memory are encoded into data files to treat images as files, and the images may be reproduced from the data files in a changed order. A memory editing function is performed, wherein files are freely edited.
As has been described above, since the digital copying machine can temporarily store images in the memory, it can perform various image editing operations which cannot be achieved by the conventional analog copying machine. Using the functions which cannot be performed by the analog machine, the digital copying machine can efficiently use various paper handling options (an automatic sheet feeder, an automatic double-side printer, a sorter/finisher, etc.).
In the above-described memory copy function, a so-called “advance-input” can be performed by using the page memory, thereby to greatly enhance productivity.
In the memory copy function, however, scanning and printing are not performed in a completely synchronous manner. Even if the user suspends a current job and performs some operation/resetting, this is not reflected on the “advance-input” image. In some cases, operability is considerably degraded, compared to the conventional analog copying machine wherein the user can smoothly perform the operational routine of starting, suspending, operating, changing of setting, and restarting.
In order to solve this problem, there is a method in which prior to the operations of suspending/restarting, data in the page memory is always erased and scanning is done once again with updated setting. However, when some change is made during the suspension, there are cases where the operation should and should not be resumed, with the data in the page memory maintained without erasing. For example, in a case where only the number of documents to be placed is changed after C/S suspension, the printing has to be resumed with use of the data remaining in the page memory.